1. Field of the Invention
The present invention relates to a dynamic random access memory (DRAM), and more particularly to a DRAM having a comparator and a method for accessing the DRAM.
2. General Background
Dynamic random access memories (DRAMs) with functions of write and read have become an important part for modern computers and personal digital systems. Referring to FIG. 3, this is a circuit diagram of a conventional DRAM. The DRAM 10 comprises a transistor 110 and a storage capacitor (Cs) 120. Typically, the transistor 110 is a thin film transistor. The transistor 110 includes a gate electrode 111, a source electrode 113, and a drain electrode 115. The Cs 120 is used for voltage access. One terminal of the Cs 120 is connected to the drain electrode 115, and the other terminal of the Cs 120 is connected to ground.
When a threshold voltage is applied to the gate electrode 111 of the transistor 110, the transistor 110 is turn on. When the transistor 110 is in the on-state, an input voltage is stored in the Cs 120 through the source electrode 113 and the drain electrode 115. Next, when the transistor 110 returns to the on-state again, the stored input voltage in the Cs 120 is read out through a path between the source electrode 113 and the drain electrode 115.
Because the transistor 110 controls the charge and discharge function for the Cs 120 as the conventional DRAM 10 is processing voltage access, a charge leakage may occur and further induce the Cs 120 and the transistor 110. This causes a shorter refresh cycle time. Therefore the refresh process is performed more frequently, and the accumulated time of the DRAM 10 device is increased. That is, the operation speed of the DRAM 10 having a transistor/capacitor structure is far slower than that of a static random access memory (SRAM) having a combination of six transistors. Compared with the SRAM, the performance of the DRAM is very inefficient. Thus there is a need for an improved DRAM structure which obviates one or more of the above-described problems, limitations and disadvantages, and provides efficient performance.